From Wikipedia:
Law & Order is an American police procedural and legal drama television series, created by Dick Wolf and part of the Law & Order franchise. It originally aired on NBC and, in syndication, on various cable networks. Law & Order premiered on September 13, 1990, and completed its 20th and final season on May 24, 2010. At the time of its cancellation, Law & Order was the longest-running crime drama on American primetime television. Its record of 20 seasons is a tie with Gunsmoke (1955–1975) for the longest-running live-action scripted American prime-time series with ongoing characters. Although it has fewer episodes than Gunsmoke, Law & Order is the longest-running full-hour series in primetime television because Gunsmoke was a half-hour in its first six seasons.
Set and filmed in New York City, the series follows a two-part approach: the first half-hour is the investigation of a crime (usually murder) and apprehension of a suspect by New York City Police Department homicide detectives; the second half is the prosecution of the defendant by the Manhattan District Attorney's Office. Plots are often based on real cases that recently made headlines, although the motivation for the crime and the perpetrator may be different.
The show has been noted for its revolving cast over the years. Among the longest-running main cast members were Steven Hill as District Attorney Adam Schiff (seasons 1–10), Jerry Orbach as Detective Lennie Briscoe (seasons 3–14), S. Epatha Merkerson as Lieutenant Anita Van Buren (seasons 4–20), Jesse L. Martin as Detective Ed Green (seasons 10–18) and Sam Waterston as Executive Assistant District Attorney (later District Attorney) Jack McCoy (seasons 5–20).
The success of the series has led to the creation of additional shows, making Law & Order a franchise, with also a television film, several video games, and international adaptations of the series. It has won and has been nominated for numerous awards over the years, including a number of Emmy Awards. On May 14, 2010, NBC announced that it had canceled Law & Order and would air the final episode on May 24, 2010. Immediately following the show's cancellation, Wolf stated that he was attempting to find a new home for the series and would also consider a "last resort" plan to conclude the show with a two-hour TV film to air on NBC. In July 2010, however, he indicated that those attempts had failed and declared that the series had now "moved to the history books".
However, in February 2015 rumors started that NBC was planning to bring the series back for 10 episodes. In May 2015, former star Sam Waterston (EADA/DA Jack McCoy) announced to "The Hollywood Reporter" that he supports and would join a revival of Law & Order, saying, "You're darn right. Sure, I'd love it. Got to break the record." Creator Dick Wolf has expressed wanting to use a L&O revival to do a 'ripped from the headlines' story-line surrounding the murder trial of Robert Durst, Wolf said "[Of all my past projects] I'd bring back Law & Order. Everybody who knows me knows it's something I want to do," he continued, "my only regret looking backward is all the great stories that we haven't been able to do for the past five years." At the 2015 Television Critics Association summer press tour, Wolf noted everyone wants a revival, "It is a question of... most of the people involved are very successful in their careers. To try to get everything in sequence is much more difficult than it looks on the outside. I am always an optimist. I would love to do it if we can make it work."